1. Field of the Invention
The present invention relates to a liquid crystal display and a driving apparatus thereof, and specifically, to an impulse driven liquid crystal display and a driving apparatus thereof for realizing moving images.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) displays images by utilizing two sheets of polarizing material with a liquid crystal layer disposed between them. An electric current passed through the liquid crystals causes the crystals to align so that light cannot pass through them. Each crystal is like a shutter, either allowing light to pass through or blocking the light. An LCD controls the luminance of the display by controlling the intensity of the light generated from the LCD, while a conventional cathode ray tube (CRT) display controls the luminance by controlling the intensity of the scanned electronic beam.
With advances in imaging technology, demand for superior displays of moving images in addition to stationary images has increased.
One problem with displaying moving images on LCDs is image dragging. This problem occurs when the response speed of liquid crystals is slower than one frame period, and image dragging results from voltages charged on one frame not being dissipated when a new voltage is applied at the next frame.
FIG. 1a is a graphical representation of wave forms for showing the relation of light density versus time of a conventional CRT, and FIG. 1b is a graphical representation of wave forms for showing the relation of light density versus time of a conventional LCD.
As shown by the spiked waveforms in FIG. 1a, the CRT is impulse driven, and the LCD is hold or level driven, as shown by the plateau wave forms in FIG. 1b. The level drive causes the image-dragging phenomenon.
One solution to remove the dragging phenomenon on the display of a LCD is by impulse driving the LCD, by inputting data for a time period less than one frame, and inputting black or white data for the remaining time of the frame.
As an example, impulse drive to an LCD can be accomplished by changing the driving frequency from 60 Hz to 120 Hz or 180 Hz. In such instances, a normal data is input to one frame (60 Hz) while black or white data is input to another frame (in the case of 120 Hz) or to two frames (in the case of 180 Hz). To implement such impulse driving, it is necessary to store one or two frames of data in a frame memory.
Since frame memories are costly, it is desirable to have a method or apparatus for impulse driving LCDs without use of frame memories.